heart rate sensor

[Ashwin K Whitchurch] and [Venkatesh Bhat] Have not missed a beat entering this year’s Hackaday Prize with their possibly lifesaving gadget HeartyPatch. The project is a portable single wire ECG machine in a small footprint sporting Bluetooth Low Energy so you can use your phone or another device as an output display.

Projects like this are what the Hackaday Prize is all about, Changing the world for the better. Medical devices cost an arm and a leg so it’s always great to see medical hardware brought to the Open Source and Open Hardware scene. We can already see many uses for this project hopefully if it does what’s claimed we will be seeing these in hospitals around the world sometime soon. The project is designed around the MAX30003 single-lead ECG monitoring chip along with an ESP32 WiFi/BLE SoC to handle the wireless data transmission side of things.

We really look forward to seeing how this one turns out. Even if this doesn’t win a prize, It’s still a winner in our books even if it only goes on to help one person.

A polygraph is commonly known as a lie detector but it’s really just a machine with a number of sensors that measure things like heart rate, breathing rate, galvanic skin response and blood pressure while you’re being asked questions. Sessions can be three hours long and the results are examined by a trained polygraph examiner who decides if a measured reaction is due to deception or something else entirely. Modern polygraphs feed data into a computer which analyses the data in real-time.

Cornell University students [Joyce Cao] and [Daria Efimov] decided to try their hand at a more old fashioned polygraph that measures heart and breathing rates and charts the resulting traces on a moving strip of paper as well as a color TFT display. They had planned on measuring perspiration too but didn’t have time. To measure heart rate, electrodes were attached to the test subject’s wrists. To measure breathing they connected a stretch sensor in the form of a conductive rubber cord around three inches long to a shoelace and wrapped this around the test subject’s abdomen.

While the output doesn’t go into a computer for mathematical analysis, it does go to a PIC32 for processing and for controlling the servos for drawing the traces on the paper as well as displaying on the TFT. The circuit between the breathing sensor and the PIC32 is fairly simple, but the output of the heart rate electrodes needed amplification. For that they came up with a circuit based off another project that had a differential amplifier and two op-amps for filtering.

Since parts of the circuit are attached to the body they made some effort to prevent any chance of electrocution. They used 12 volts, did not connect the test subject to power supply chassis ground, and tested the heart rate electrodes with a function generator first. They also included DC isolation circuitry in the form of some resistors and capacitors between the heart rate electrodes and the amplifier circuit. You can see these circuits, as well as a demonstration in the video below. The heart rate output looks a little erratic, no surprise given that the body produces a lot of noise, but the breathing trace looks very clear.

[Eduardo] contacted us about his success at connecting a blood pressure monitor to the web. He pulled this off by locating the chip responsible for storing the blood pressure data after being measured. It was a simple I2C EEPROM from which he dumped the data a sniffed communications with a 4 bit logic analyzer. [Eduardo] published all of his findings on that communication scheme so check out his post for more on that. The gist of it is that he implemented his reverse engineered protocol using an ESP8266, the ubiquitous cheap WiFi board that has become a go-to for web-connected anything like power monitors and underpowered but awesome server farms. Check out the Hackaday Dictionary entry for more on this board.

[Eduardo] is not the first on the scene with such a device, you can see a Withings device and a blipcare device available on Amazon. What this hack from [Eduardo] does provide is evidence of a much cheaper route for connecting vital medical data from a geographically distant, and perhaps technophobic family member. Lets take a walk down hypothetical lane, shall we? Uncle Bob in Albuquerque who doesn’t have any local family might be a good candidate for such a hacked device, everyone knows it’s like pulling teeth to get elderly family members to report some health information to loved ones… but with [Eduardo’s] hack it’s simple. Embed the hardware (assuming you know the login creds ahead of time) into a new BPM, send it to him as a gift, and Bob’s your uncle.

Look around for heart rate sensors that interface easily to microcontrollers, and you’ll come up with a few projects that use LEDs and other microcontrollers to do the dirty work of filtering out pulses in a wash of light.

[Thomas] was working on a project that detects if water is flowing through a pipe with a few piezoelectric sensors. Out of curiosity, he taped the sensor to his finger, and to everyone’s surprise, the values his microcontroller were spitting out were an extremely noise-free version of his heart rate.

The piezo in question is a standard, off the shelf module, and adding this to a microcontroller is as easy as putting the piezo on an analog pin. From there, it’s just averaging measurements and extracting a heartbeat from the data.

It’s a much simpler solution to measuring a heart rate, and since two people haven’t heard of this technique, it’s likely a lot more people haven’t heard of this technique either. If you’re looking for an entry to The Hackaday Prize, this would be a great jumping off point for anything in either the fitness or medical domains.